Support for Raspberry Pico

[saleema90]

If running into issue with building the loader for pico:

[saleema90]

zephyr/boards/raspberry/rpi_pico/rpi_pico_common.dtsi file needs to be updated:

zephyr,code-partition = &user_sketch;
...
user_sketch: partition@100 {
label = ""user_sketch";
....
}